A meta-analysis of conservation tillage management effects on soil organic carbon sequestration and soil greenhouse gas flux.

Conservation tillage practices, including reduced tillage (RT), no-tillage (NT) and straw return (SR), have been widely adopted to enhance soil organic carbon density (PSOC) and improve the soil quality while mitigating the negative environmental impacts of intensive farming. However, current studies on the effects of these practices on SOC sequestration and N2O flux show considerable variability, making it challenging to draw definitive conclusions about the individual and combined impacts of conservation tillage practices and introducing substantial uncertainty in estimating the agricultural sector's potential to mitigate climate change. To address this gap, we conducted a meta-analysis of 902 pairwise comparisons from 90 peer-reviewed publications to evaluate the effects of five conservation tillage practices (straw return (SR), reduced tillage (RT), no-tillage (NT), straw return combined with tillage reduction (SR + RT) and straw returning combined with no-tillage (SR + NT)) on C sequestration and N2O emissions from agricultural soils. The results show that SR was the most effective practice for increasing SOC content (23.7 %), followed by RT + SR (5.5 %) and NT + SR (4.4 %). Additionally, RT (12.3 %) and NT (14.3 %) significantly reduced soil N2O emissions. This study also identified key drivers, including climatic factors, soil properties, and agricultural management practices, that influence SOC content and N2O emissions under different conservation tillage practices. For example, the mean annual precipitation, mean annual temperature, soil type, pH, soil total nitrogen content, N application rate, and experiment duration were identified as the key factors affecting SOC content and N2O emissions Specifically, suitable temperature, lower rainfall and alkaline soil environment significantly enhanced the C sequestration efficiency of SR, while suitable climatic conditions and soil texture combined with an alkaline environment contributed to a significant reduction in long-term NT soil N2O emissions. These results provide a robust scientific foundation for the strategic implementation of conservation tillage to reduce greenhouse gas emissions, mitigate global warming, and enhance soil C sequestration capacity.

Water Management-Mediated Changes in the Rhizosphere and Bulk Soil Microbial Communities Alter Their Utilization of Urea-Derived Carbon.

As one of the most important fertilizers in agriculture, the fate of urea-derived nitrogen (urea-N) in agricultural ecosystems has been well documented. However, little is known about the function of urea-derived carbon (urea-C) in soil ecosystems, especially which soil microorganisms benefit most from the supply of urea-C and whether the utilization of urea-C by the rhizosphere and bulk soil microorganisms is affected by irrigation regimes. To address this, a soil pot experiment was conducted using 13C-labeled urea to investigate changes in the composition of the rhizosphere and bulk soil microbial communities and differences in the incorporation of urea-derived C into the rhizosphere and bulk soil phospholipid fatty acids (PLFA) pool under flooded irrigation (FI) and water-saving irrigation (CI). Our results suggest that the size and structure of the rhizosphere and bulk soil microbial communities were strongly influenced by the irrigation regime. The CI treatment significantly increased the total amount of PLFA in both the rhizosphere and bulk soil compared to the FI treatment, but it only significantly affected the abundance of Gram-positive bacteria (G+) in the bulk soil. In contrast, shifts in the microbial community structure induced by irrigation regimes were more pronounced in the rhizosphere soil than in the bulk soil. Compared to the FI treatment, the CI treatment significantly increased the relative abundances of the G+ and Actinobacteria in the rhizosphere soil (p < 0.05). According to the PLFA-SIP, most of the labeled urea-derived C was incorporated into 16:1ω7c, 16:0 and 18:1ω7c under both treatments. Despite these general trends, the pattern of 13C incorporation into the PLFA pool differed between the treatments. The factor loadings of individual PLFAs suggested that 18:1ω7c, 16:1ω7c and 16:1ω5c were relatively enriched in urea-C in the bulk soil, while 17:1ω8c, i16:0 and 16:0 were relatively enriched in urea-C in the rhizosphere soil under different irrigation regimes. The loadings also confirmed that 10-me16:0, cy17:0 and cy19:0 were relatively enriched in urea-C under the CI treatment, whereas 14:0, a15:0 and 15:0 were relatively enriched in urea-C under the FI treatment. These results are helpful not only in revealing the interception mechanism of urea-C in soil but also in understanding the functions of key microbes in element cycles.

Nitrous oxide (N2O) emission characteristics of farmland (rice, wheat, and maize) based on different fertilization strategies.

Fertilizer application is the basis for ensuring high yield, high quality and high efficiency of farmland. In order to meet the demand for food with the increasing of population, the application of nitrogen fertilizer will be further increased, which will lead to problems such as N2O emission and nitrogen loss from farmland, it will easily deteriorate the soil and water environment of farmland, and will not conducive to the sustainable development of modern agriculture. However, optimizing fertilizer management is an important way to solve this problem. While, due to the differences in the study conditions (geographical location, environmental conditions, experimental design, etc.), leading to the results obtained in the literatures about the N2O emission with different nitrogen fertilizer application strategies have significant differences, which requiring further comprehensive quantitative analysis. Therefore, we analyzed the effects of nitrogen fertilizer application strategies (different fertilizer types and fertilizer application rates) on N2O emissions from the fields (rice, wheat and maize) based on the Meta-analysis using 67 published studies (including 1289 comparisons). For the three crops, inorganic fertilizer application significantly increased on-farm N2O emissions by 19.7-101.05% for all three; and organic fertilizer increased N2O emissions by 28.16% and 69.44% in wheat and maize fields, respectively, but the application of organic fertilizer in rice field significantly reduced N2O emissions by 58.1%. The results showed that overall, the application of inorganic fertilizers resulted in higher N2O emissions from farmland compared to the application of organic fertilizers. In addition, in this study, the average annual temperature, annual precipitation, soil type, pH, soil total nitrogen content, soil organic carbon content, and soil bulk weight were used as the main influencing factors of N2O emission under nitrogen fertilizer strategies, and the results of the study can provide a reference for the development of integrated management measures to control greenhouse gas emissions from agricultural soils.

The effect of biochar types on carbon cycles in farmland soils: A meta analysis.

Application of biochar has been demonstrated to be a successful strategy for boosting soil carbon sequestration and altering the agricultural soil carbon cycle. However, in the studies involving biochar worldwide, the effects of different types of biochar on the soil carbon component response direction and increase are not consistent. Therefore, to assess the effects of applying four types of biochar during the soil carbon cycle on carbon components on a farmland, we performed a meta-analysis of 1150 comparisons from 86 peer-reviewed publications. Generally speaking, the types of biochar raw materials have a significant impact on soil carbon cycle. The application of chaff biochar significantly inhibited (10.0 %) soil respiration, while the application of manure biochar (47.0 %), straw biochar (11.2 %) and wood biochar (8.7 %) showed a strong promotion effect on CO2 emission. In addition, although the soil organic C, microbial biomass C and dissolved organic C all had positive responses to the application of the four biochar types, the degree and increase in their response varied greatly due to the differences in biomass raw materials. Moreover, by increasing the biochar rates applied to coarse-textured soils with low average annual rainfall and an average temperature under controlled circumstances, the relative increase in SOC was encouraged. Meanwhile, applying low temperature pyrolytic biochar (≤400 °C) at a lower rate (<25 t/ha) in the long-term experiment (>3 years) is more beneficial to soil C sequestration and emission reduction. Hence, climatic conditions, agricultural management practices, and initial soil properties jointly constrained and influenced the ability of biochar to alter the soil C cycle. Based on this, our research offers a fresh viewpoint for making a profound study biochar-enhanced soil C cycle.

Response of Wheat, Maize, and Rice to Changes in Temperature, Precipitation, CO2 Concentration, and Uncertainty Based on Crop Simulation Approaches.

The influence of global climate change on agricultural productivity is an essential issue of ongoing concern. The growth and development of wheat, maize, and rice are influenced by elevated atmospheric CO2 concentrations, increased temperatures, and seasonal rainfall patterns. However, due to differences in research methodologies (e.g., crop models, climate models, and climate scenarios), there is uncertainty in the existing studies regarding the magnitude and direction of future climate change impacts on crop yields. In order to completely assess the possible consequences of climate change and adaptation measures on crop production and to analyze the associated uncertainties, a database of future crop yield changes was developed using 68 published studies (including 1842 samples). A local polynomial approach was used with the full dataset to investigate the response of crop yield changes to variations in maximum and minimum temperatures, mean temperature, precipitation, and CO2 concentrations. Then, a linear mixed-effects regression model was utilized with the limited dataset to explore the quantitative relationships between them. It was found that maximum temperature, precipitation, adaptation measure, study area, and climate model had significant effects on changes in crop yield. Crop yield will decline by 4.21% for each 1 °C rise in maximum temperature and increase by 0.43% for each 1% rise in precipitation. While higher CO2 concentrations and suitable management strategies could mitigate the negative effects of warming temperatures, crop yield with adaptation measures increased by 64.09% compared to crop yield without adaptation measures. Moreover, the uncertainty of simulations can be decreased by using numerous climate models. The results may be utilized to guide policy regarding the influence of climate change and to promote the creation of adaptation plans that will increase crop systems' resilience in the future.

Xylem vessel type and structure influence the water transport characteristics of Panax notoginseng.

Panax notoginseng plays a very important role in medicinal and economic value. The restriction imposed by the hydraulic pathway is considered to be the main limitation on the optimal growth state of Panax notoginseng. The flow resistance and water transport efficiency of vessel were affected by vessel type and secondary thickening structure. The vessel structure parameters of Panax notoginseng were obtained by experimental anatomy, and the flow resistance characteristics were analyzed by numerical simulation. The results showed that the xylem vessels had annular thickening and pit thickening walls. The flow resistance coefficient (ξ) of the pitted thickening vessel was significantly lower than that of annular thickening vessel in four cross-sectional types. The ξ of the circular cross-sectional vessel was the largest, followed by the hexagon, pentagon cross-sectional vessel and the lowest was the quadrilateral cross-sectional vessel, and the structure coefficient (S) was just the opposite. The ξ of the vessel model was positively correlated with the annular height, pitted width and pitted height, and negatively correlated with the annular inscribed circle diameter, annular width, annular spacing, pitted inscribed circle diameter and pitted spacing. Among them, annular (pitted) height and the annular (pitted) inscribed circle diameter had a great influence on the ξ. The increasing and decreasing trend of the S and ξ were opposite in the change of annular (pitted) inscribed circle diameter, and consistent in the change of in other structural parameters, indicating that the secondary wall thickening structure limited the inner diameter of the vessel to maintain a balance between flow resistance and transport efficiency.

Organic fertilizer substitutions maintain maize yield and mitigate ammonia emissions but increase nitrous oxide emissions.

Organic fertilizer can improve soil structure and enhance the nutrient content in soil and is beneficial to sustainable agricultural development. However, the influence of organic fertilizer substitutions on NH3 and N2O emissions from farmland is unclear. Thus, we set up an organic substitution field experiment in Northeast China. The experiment included six treatments: single application of chemical fertilizers (NPK: 250 kg N ha-1); NO10, 10% reduction in chemical nitrogen fertilizers (225 kg N ha-1) + chicken manure (25 kg N ha-1); NO20, 20% reduction in chemical nitrogen fertilizers (200 kg N ha-1) + chicken manure (50 kg N ha-1); NO30, 30% reduction in chemical nitrogen fertilizers (175 kg N ha-1) + chicken manure (75 kg N ha-1); NO40, 40% reduction in chemical nitrogen fertilizers (150 kg N ha-1) + chicken manure (100 kg N ha-1); and no-nitrogen fertilizer (CK). This experiment investigated the effects of partial substitution of chemical nitrogen fertilizer with organic fertilizer on NH3 and N2O emissions and nitrogen use efficiency in a maize field. The results showed that, compared with chemical N, organic fertilizer mitigated NH3 volatilization but promoted the soil N2O total emissions during the whole growth stage. NH3 cumulative volatilization decreased with the increase in the substitution rate of organic fertilizer. Compared with the NPK treatment, the cumulative volatilization of NH3 in the NO30 and NO40 treatments decreased by 15.24 and 17.92%, respectively. The NO40 treatment had the highest N2O emission in the whole growth stage, and the N2O emission of the NO40 treatment increased by 10.72% compared to the NPK treatment. Moreover, the yield, partial factor productivity (PFP), nitrogen harvest index (NHI), and apparent nitrogen recovery efficiency (NRE) of NO30 treatment were the highest of all treatments, and the yields, PFP, plant N accumulation, grain N accumulation, and the cumulative emissions of NH3 and N2O were similar to N20 treatment. In conclusion, nitrogen fertilizer use efficiency was enhanced, decreasing environmental pollution from livestock under organic fertilizer substitution conditions. We suggested 20% or 30% substitution rates of organic fertilizer were proper.

Structural optimization and hydraulic performance analysis of bionic pit flow channels based on a genetic algorithm.

Orthogonal experiments have mostly been used in the structural optimization of drip irrigation emitter flow channels. To further improve the efficiency of the optimal design, this study used a genetic algorithm to optimize the structure of the bionic pit flow channel. Based on the structural similarity and performance optimization of the torus-margo bordered pit structure, the constitutive equation of the flow channel unit was constructed. The selection, crossover and mutation operators were set by the genetic algorithm, and the objective function value was calculated. The design variables and known variables that met the requirements were put into the computational domain model, and the pit flow channel structure was simulated and optimized. The results showed that there were large low-velocity regions at the junctions and corners of the pit flow channel units at a working pressure of 50 kPa, and no complete low-velocity vortices were observed, indicating that the flow channels had good anti-clogging performance. The distribution of flow velocity on the same cross-section was quite different, which made the flow layers collide and mix, which intensified the loss of energy, indicating that it had a good energy dissipation effect. The multivariate linear regression analysis showed that the four variables of tooth stagger value (j), flow channel angle (θ), tooth spacing (l) and inner and outer boundary spacing (h) had a decreasing degree of influence on the flow index (x). The flow index (x) was negatively correlated with the tooth stagger value (j), flow channel angle (θ) and tooth spacing (l), and positively correlated with the inner and outer boundary spacing (h). The test results of physical samples showed that the average error between the simulation results and the real values was 3.4%, indicating that the accuracy was high, which can provide a basis for the structural optimization design of related pit drip irrigation emitters.

Effects of different water management and fertilizer methods on soil temperature, radiation and rice growth.

In recent decades, the application of organic fertilizer to agricultural soils has attracted wide attention. However, few studies have carefully explored the effects of humic acid fertilizer on soil temperature, radiation, and the physiology of plant leaves, especially when coupled with different irrigation methods. To provide a better growing environment for crops and explore the best regulation method of humic acid fertilizer and irrigation in the farmland soil environment on the Songnen Plain, China, through field experiments, we selected rice as the test crop and applied humic acid fertilizer to the soil with different irrigation methods. The effects of different humic acid fertilizers and irrigation methods on the soil temperature and radiation changes during different growth stages were examined, and the subtle differences in agronomic and fluorescence characteristics in different growth stages of rice plants were compared. The results showed that the soil temperature was not significantly different among all the treatments. However, radiation interception was obviously different, and the best value was observed in the CT5 treatment. The fluorescence indices and leaf chlorophyll relative content (SPAD) differed with the change in humic acid fertilizer application and irrigation methods. At the jointing and heading stages, the Fv /Fm values of the CT5, FT5 and WT5 treatments were larger than those of the other treatments, and the best value was recorded in the CT5 treatment. The differences in NPQ at these two stages were significant, and the NPQ in the CT5 treatment was significantly higher than that in the other treatments (P < 0.05). In general, the QP under control irrigation was greater than that under flood and wet irrigation (P < 0.05). Moreover, there were no significant differences among the gradients under the different humic acid fertilizer application methods in terms of QP (P > 0.05). Additionally, SPAD values were higher under the CT5 and FT5 treatments.

Flow resistance characteristics of the stem and root from conifer (Sabina chinensis) xylem tracheid.

Xylem tracheids are the channels for water transport in conifer. Tracheid flow resistance is composed of tracheid lumen resistance and pit resistance. The single tracheid structure parameters in the stem and root of Sabina chinensis were obtained by dissociation and slicing, combined with numerical simulation to analyze the tracheid flow resistance characteristics. The results showed that the tracheid lumen resistance was determined by the tracheid width and tracheid length. The pit resistance was determined by the number of pits and single pit resistance. The single pit resistance was composed of four elements: the secondary cell wall, the border, the margo and the torus. The margo contributed a relatively large fraction of flow resistance, while the torus, the border and the secondary cell wall formed a small fraction. The size and position of the pores in the margo had a significant effect on the fluid velocity. The number of pits were proportional to tracheid length. The power curve, S-curve and inverse curve were fitted the scatter plot of total pit resistance, total resistance, total resistivity, which was found that there were the negative correlation between them. The three scatter plot values were larger in the stem than in the root, indicating that the tracheid structure in the root was more conducive to water transport than the stem. The ratio of tracheid lumen resistance to pit resistance mainly was less than 0.6 in the stem and less than 1 in the root, indicating that the pit resistance was dominant in the total resistance of the stem and root.